The invention relates to a flame retardant comprising a phosphorus compound and comprising a sulfur compound, and to a polymer composition, in particular in the form of foam, comprising the flame retardant, to processes for producing the polymer composition, and to the use of the foamed polymer composition as insulation material.
The provision of flame retardants to polymers, in particular to foams, is important for a wide variety of applications, examples being molded polystyrene foams made of expandable polystyrene (EPS), or extruded polystyrene foam sheets (XPS), for insulating buildings.
The flame retardants currently used in plastics are mainly polyhalogenated hydrocarbons, optionally in combination with suitable synergists, for example organic peroxides or nitrogen-containing compounds. A typical representative of these traditional flame retardants is hexabromocyclododecane (HBCD) which is used by way of example in polystyrene. The plastics industry is making major efforts to replace halogenated flame retardants for reasons of bioaccumulation, and also because of the persistence properties of some polyhalogenated hydrocarbons.
DE-A 16 94 945 has proposed combinations of sulfur with bromine compounds and with phosphorus compounds as flame retardants for polystyrene foams.
EP-A 0 806 451 discloses, alongside elemental sulfur, dialkyl polysulfides as synergists for organophosphorus flame retardants for use in expanded (EPS and XPS) polystyrene foams.
WO 2009/035881 describes phosphorus-sulfur compounds which optionally have di- or polysulfide groups.
Although the known systems are already achieving good results, there is much scope for improvements, particularly in relation to production, performance characteristics, and interactions between associated additions in the materials requiring protection. By way of example, increased amounts of the conventional flame retardant HBCD have to be used when athermanous substances such as chalk or graphite are also present.